Method for the electrolytic removal of drawing or rolling lubricants on steel strands

ABSTRACT

A one-step method for the removal of drawing or rolling lubricants from metal strands is described, in which the strands are subjected to an electrolytic treatment at a current density of 30-60 amps/in2 in an aqueous bath which contains about 6 to 16 wt. percent NaOH, .5 to 6% Na4P2O7 and .5 to 5% Na2CO3.

United States Patent Sallo et al.

[ 51 June 6,1972

[54] METHOD FOR THE ELECTROLYTIC REMOVAL OF DRAWING OR ROLLING LUBRICANTS ON STEEL STRANDS 721 Inventors: Richard L. Sallo, Greensburg'charles I). Stricker, Monroeville Borough, both of [73] Assigneez' United States Steel Corporation [22] Filed: Apr. 20, 1970 211' App]. 140.; 30,358

52 u.s.c1.' 204/1451: 51 1m.c1. c231 1/04 58 FieldofSearch ..204/145R Primary Examiner-John H. Mack Assistant Examiner-T. Tufariello Attorney-Arthur J. Greif 57 ABSTRACT A one-step method for the removal of drawing or rolling lubricants from metal strands is described, in which the strands are subjected to an electrolytic treatment at a current density of 30-60 amps/in in an aqueous bath which contains about 6 to 16 wt. percent NaOH, .5 to 6% Na,P O, and-.5 to 5% Na CO 5 Claims, No Drawings METHOD FOR THE ELECTROLYTIC REMOVAL OF DRAWING OR ROLLING LUBRICAN'IS ON STEEL STRANDS Selection of a cleaning process to be employed is largely influenced by the type of soil to be removed and the subsequent finishing operation to be employed. In order to provide a clean, active surface as a base for coating metal strands (wire, rod, strip), the methods using acid pickling or acid electropickling have proven to be inadequate, since acid alone will not remove either the water soluble or water insoluble lubricants which are generally utilized in drawing or rolling operations. An effective methodfor lubricant removal has been a process in which the lubricant on the strand is "charred" at.

- these operations require relatively long electrocleaning cells (e.g. of 60 feet length) and long immersion times (e.g. of 30 to 60 seconds). This latter method suffers from an additional drawback in that the quality of cleaning is often marginal, with difficulties being experienced in subsequent coating operations. Therefore, when complete cleaning has been required, it has generally been necessary to employ an intermediate or additional cleaning step to attain the desired results. Thus, a typical mill practice for electrogalvanizing cold rolled steel strapping requires an electroalkaline cleaning for 15 seconds at 100 amps/ft (0.7 amps/in") using a commercial alkaline cleaner, followed by a hydrochloric acid pickle, a flash plate from a zinc cyanide bath for seconds (cyanide strike) and a rinse prior to being galvanized. It has-been found that, when the high current density method of the instant invention is utilizcd, the cyanide strike may be eliminated and yet a coating is obtained in which the adhesion and continuity is at least as good as that 'of the standard practice. i

It is therefore an object of this invention to provide a onestep method for effectively cleaning metal-strands.

A further object of this invention is to provide a cleaning treatment which will provide improved adhesion of subsequent coatings. v v

Another object is to provide a cleaning process which eliminates the necessity for additional cleaning steps employed to compensate for inadequate prior art electroalkaline cleaning. I I

These and other objects are accomplished by employing an electroalkaline'cleaning process in which the strands are electrolyzed at a current density of from 30 to 60 amps/in in an electrolyte containing a mixture of 6 to 16% NaOH, 0.5 to 6% Nay- .0, and 0.5 to Na CO for an immersion time of atleast 0.4 seconds. Lubricant films which have been satisfactorily removed by the instant method include oils, greases, and water-soluble soaps and lubricant carriers. The criticality of the above parameters and other aspects of the invention will become more apparent by referring to the following detailed description.

To determine the optimum current density required for effective removal, a series of tests was run, at a constant potential of 20 volts (except as noted) in which different currents were obtained due to the differences in conductivity of the electrolyte employed. in each test, the wire was electrolyzed for one second as a cathode, followed by one second as an anode. The wire samples employed were drawn to the process size by using borax as the lubricant carrier and sodium stearate as the lubricant. The effectiveness of the cleaning operation was determined by the degree of adhesion which was obtained in a subsequent electroless plating with CuSO After the copper plating, the amount of copper which could be rubbed off the test sample was noted and was rated on a l to 4 basis, with 4 representing total vadherence and l representing poor adherence (i.e. large amount of plating rubbed Ofl).

It may be seen from the above-that for satisfactory and rapid removal of lubricant films, high current density electro-cleaning provides a substantial improvement, as evidencedby the enhanced adherence of the copper plate. ln addition to providing a more complete removal of lubricants, high current densities are advantageous in two other respects; l they permit higher operating speeds and shorter cleaning cells, due to the considerably faster removal which is achieved, and (2) they are more etficient than low current densities, i.e., they provide equivalent cleaning with less energy expended. Illustrative of this latteradvantage, the degree of removal achieved at 40 A/in for 0.4 seconds (16 coul/in) is'at least as good as the results obtained when the prior art practice is employed, i.e. applying 1 A/in for 60 seconds (60 coullin or a ratio of energy expended of almost 1 to 4.

It may also be seen from Table 1 above that-in order to obtain the necessary high current densities required for totally effective cleaning, the conductivity of the electrolyte must be considerably higher than that ordinarily employed in electroalkaline cleaning. Apreferred electrolyte is a'mixture containing 60 to NaOH or an equivalent high conductivity alkali hydroxide, 5 to 30% Na P,O, and 5 to 25% Na Co This mixture (to which a non-foaming surface active agent may be added to promote wetting of the strand) is dissolved in water to a concentration of 10 to 20% by weight and during operation is maintained within a temperature range of to 210 F. Other well-known builders may be substituted for the above components, tag. the sesquicarbonate for the carbonate and trisodium phosphate or the tripolyphosphate for the tetrasodium pyrophosphate. It is, of course, essential that the solution possess sufficient conductivity to permit electrolyzation with a current density of at least 30 amps/in.

To avoid arcing at the highcurrent densities employed, the electric current is introduced to the strand via the electrolyte. A preferred apparatus for the instant process is that described in US. Pat. No. 3,338,809, in which the electrodes surround .the strand without actually contacting it. in employing the contact time of greater than 2.5 seconds is less desirable for economic considerations and does not appear to provide any enhanced cleaning. Therefore, in order to attain this minimum immersion time as line speed is increased, it will be necessary to likewise increase the number of cell chambers. The polarity is such that the strand will be anodic in the final chamber, thereby avoiding the danger of electrolyte contaminates plating out on the treated strand.

We claim:

1 A method for the cleaning of ferrous strands and the a removal of lubricants therefrom which comprises electrolyzing said strand with a direct current at a current density of 30 I to tSO ampsIin for an immersion time of at least 0.4 seconds, in

3. The method of claim 2, in which the current is introduced to the strand via said electrolyte, and said current density is at least 45 amps/in.

4. The method of claim 3, in which the polarity of the strand is reversed as it passes through a series of treatment zones, with the polarity of the strands being anodic in the final treatment zone.

5. The method of claim 3, wherein said lubricants are selected from the group consisting of oils, greases and watersoluble soaps and carriers. 

2. The method of claim 1, in which the electrolyte is maintained at a temperature of 160* to 210* F and consists essentially of from 10 to 20 percent by weight of a mixture of 60 to 80% NaOH, 5 to 30% Na4P2O7 and 5 to 25% Na2CO3.
 3. The method of claim 2, in which the current is introduced to the strand via said electrolyte, and said current density is at least 45 amps/in2.
 4. The method of claim 3, in which the polarity of the strand is reversed as it passes through a series of treatment zones, with the polarity of the strands being anodic in the final treatment zone.
 5. The method of claim 3, wherein said lubricants are selected from the group consisting of oils, greases and water-soluble soaps and carriers. 